If higher engine RPM's are required to get started, you may just use the throttle pedal instead.

If the fast idle is rigged, that works, but I suspect that with a little practice, you can get it moving on a slope with less wear to the clutch by way of less throttle than fast idle.

Your goal for longest clutch life is to have as little difference in rotating speeds between the engine and the drive train in order to get the coach moving, or while shifting gears.

Just think of there being a big grinding wheel in there, the faster the rate of spin, the more material you remove.

Hence, the much encouraged dead throttle start, with the engine only on the idle, and the governor to keep it there, has the lowest spin speed in relation to a stationary drive train.

As for the safety of a fast idle feature able to be engaged while underway, I suppose that if we can think of an inopportune time for the engine to be allowed higher rpm's, or to have the throttle pedal locked out with the parking brake released, that would be it?

All the GMC parlor and transit buses up thru the 4106s came from the factory with "Johnson bar" mechanical parking brakes. All later model GMs came with push/pull air-operated parking brakes (DD3s).

The fast idle circuit is wired into the parking brake with a switch that kills the fast idle when the bar is moved beyond a certain point as you release it. Or, at least that's the way it was wired when it came from the factory.

As Tom mentioned, his switch apparently has been by-passed (Gus's & Rick's too?) by a previous owner.

Every bus I've ever had any experience with that was equipped with the push/pull parking brake always killed the fast idle when the brake was released.

While working in revenue service with manual transmission coaches, I never ran across a situation where I couldn't get the bus rolling in first gear on most small inclines. Even when having to stop on a grade to hang chains on the drive axle. I will admit to stalling the engine a few times, but with more practice, stalls became fewer and the starts more smooth. It's all in the techique, training and practice. I happened to have a great instructor early in my bus driving career - she taught me well!

Tip: Remember that the service brake release delay can be your friend when starting on a grade. (Think about it!)

While it sounds like it is possible to restart up a grade with a 4104 or 4106 with a spicer tranny, would a 4106 with a Alison auto be the "best" case scenario? One of your replies mentioned having to back down the mountian... with a toad. That would be a nightmare.

On the flip side of this, how well does a Alison V-730 handle going down the mountain?

There is no "free-wheeling" with the v730, it shifts up/down by rpms, and will hold it's gear for the rpm range it is in. It also locks up in 2nd and 3rd so there is a solid mechanical coupling just like a manual. Tom can actually do a better job with these details. I have Jake brakes on mine, and with the light weight of the 4106, they allow long steep descents without ever touching the brakes. There is no disputing the fact that it is a great mountain setup, and an inexpensive one at that.

I have never driven one, but I understand that the VS series Allison will give an exciting ride down hill. Maybe someone who knows can clarify how it performs.

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L. Christley - W3EYE Amateur ExtraBlue Ridge Mountains, S.W. VirginiaIt’s the education gained, and the ability to apply, and share, what we learn.Have fun, be great, that way you have Great Fun!

We have never been bothered very much by backing down a hill , except by an impatient motorist who couldn't wait to go around us. Part of the reason is that we have never towed. Backing in good light is not much of a problem. Doing it at night is another problem, altogether. Good backup lights are needed that did not come on the 4106.

The danger of using the fast idle would be the amount of damage a bus could do if the driver lost control on fast idle. If it stayed on slow idle, it wouldn't take much damage to kill the engine, by comparison.

We go up slopes that break over 20%, but I consider it mandatory to run the coach against the governor, starting from the beginning of the steep part and going all the way to the top without easing up on the throttle.

Powerful solutions have powerful hazards is the way I see it. Take care.

20% boggles my mind. I had a hill like that stop Wendy and I was only pulling a 2800 pound Datsun Z car. To her credit and my amazement, I found the next day that she had shed a plug wire so she quit half way up on 7 but probably would have squeaked over the top with all eight firing. Want a fun time? Try unhooking a car while it is dangling off of a ball. Now don't insult me with "you should just have....". I'll repeat the story in OT some time in the future and till then I would actually appreciate yours and anyone's suggestion on how to achieve that separation of "iron".

John

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To me "fast idle" is no more than part throttle except that you can have it while you are parked without having to have your foot on the accelerator.

My bus doesn't have fast idle but even if it did the last thing I would want when starting out is "less" control of the throttle which is what you have on fast idle. When I have to start on a grade I give it some throttle(more than usual) and engage the clutch as fast as possible without stalling it. And as I am letting out the clutch I am also easing up on the throttle aiming for the quickest "full clutch engagement" as possible.

Riding the clutch (or part engagement) to me is the worst thing you can do.

What always worries me about an automatic, is how slow you can go before the converter unlocks. Most automatics I've drive (newer buses) can't seem to go below 30mph before unlocking 2nd. I'd be really worried about overheating climbing a long steep grade with unlocked automatic.

My bus is fortunate enough to have a 6.1:1 crawler 1st, so I can easily start on just about any gear. In 3rd at around 25mph and 2100rpm, my little 6v71 would climb almost ANY grade, partial throttle, no smoke and no overheating, for any lenth of time.

Wow, a lot of different thoughts here, seems the method I described in my earlier post is not a very popular procedure.

I will try and give a better explanation of what I have done several times when starting my 4104 out on a grade. It has worked for me with no clutch slippage several times in the past.

I set the brakes (spring), put the clutch in, put the transmission in first, engage fast idle and as I let the clutch out release the brakes and as soon as the coach begins to move quickly switch off fast idle and get on the foot throttle. It all happens pretty quick and is a very smooth start with no clutch slippage. Maybe this is not the correct way but as I said it works great for me.

I drive a big truck 5 nights a week hauling US Mail, just got in tonight with a 75,000 lb load and have used a method close but somewhat different to this for years to get the big truck moving from a stop on a grade when I have a heavy load. No clutch problems as of yet.

I set the brakes (spring), put the clutch in, put the transmission in first, engage fast idle and as I let the clutch out release the brakes and as soon as the coach begins to move quickly switch off fast idle and get on the foot throttle. It all happens pretty quick and is a very smooth start with no clutch slippage. Maybe this is not the correct way but as I said it works great for me.

Your method sounds good to me. If you used the spring brake, do you have to use the fast idle to get the RPM's up since you don't have to use the air break? When I had my 4104 I don't remember using the mechanical break on an incline, so I really don't know how well it would work.

The few times I have done what I described in my last post I have been in heavy traffic on a short but pretty steep grade with a car stuck like glue on my rear bumper..... a situation where I had to stop somewhere I normally would not stop. It is not something I do or feel I need to do everytime I start the coach rolling on a hill.

It usually happens to me in the Branson Mo. area. If you have ever been to Branson I think you will know what I am talking about....I avoid Branson's highway 76 strip but any time I am up there it seems to happen, I get stopped on a hill in traffic somewhere I would rather not be. This has gotten me out of a tight spot more than once but I would recommend practicing it a few times without the traffic and the mental pressure the traffic and finding youself in a bad situation will put on you. I am no expert here just telling what has worked for me.

On my MCI the fast idle can only be engaged if the parking brake is on. If you release the parking brake, fast idle is automatically disengaged. Also, when fast idle is on the accelerator pedal is locked out. You cannot use the accelerator pedal for anything other than a foot rest when fast idle is on. Given those two things, using fast idle to help you start on a grade is a non-starter, it just can't happen.

What I have done in the past is use the parking brake. On my bus (may not work on all, although I am developing a technique that needs field trial...) I can engage the parking brake with the push pull valve and disengage by pushing it in and the DD3's release on their own with no brake pedal application. That lets me feather the throttle up and engage the clutch at a slightly higher rpm.

Of course being a racing car driver I also have a tendency to heel and toe the brake and the throttle simultaneously, although that is kinda hard with those pedals...